The present invention disclosed herein relates to a photonic device, and more particularly, to a waveguide structure capable of reducing temperature-dependent wavelength shift (TDWS).
The present invention has been derived from research undertaken as a part of the information technology (IT) development business by the Ministry of Information and Communication and the Institute for Information Technology Advancement of the Republic of Korea [Project management No.: 2006-S-004-02, Project title: silicon based ultra high speed optical interconnection IC].
Optical interconnection technology can be used to realize a high speed bus of a semiconductor device such as a central processing unit (CPU). A wavelength-division-multiplexing (WDM) device capable of selectively dividing a predetermined wavelength of light is required to exchange signals through the optical interconnection technology.
Because a ring resonator can selectively extract light with a predetermined wavelength by the use of optical resonance phenomenon, it can be used for a WDM device. For example, a method of selectively extracting light with a predetermined wavelength is disclosed in a paper by W. Bogaerts et al. (“Compact Wavelength-Selective Functions in Silicon-on-Insulator Photonic Wires,” IEEE J. Selected Topics in Quantum Electronics, vol. 12, no. 6, 2006.). In more detail, as illustrated in FIG. 1, this paper of W. Bogaerts discloses a method of minutely adjusting radii of rings 11, 12, 13, and 14 to selectively extract lights with various wavelengths λ1, λ2, λ3 and λ4 (that is, r1<r2<r3<r4).
However, silicon has a thermo-optic coefficient (TOC) of 0.00018/° C., which is about 18 times that of silica (SiO2). Herein, the TOC represents a change in refractive index with temperature. Accordingly, a silicon ring resonator has a TDWS ranging from about 80 pm/° C. to about 100 pm/° C., which may not be appropriate for an actual product.
To reduce such a high TWDS, a method of forming a channel waveguide using silica or polymer for a cladding may be considered. This method is effective in a silica WDM device, whereas it is not available for a WDM device based on silicon having a high TOC because this method cannot effectively suppress the TDWS in the silicon WDM device. Especially, most of an optical mode is distributed inside a silicon core in a channel waveguide structure of a silicon WDM device, and thus a method of forming a cladding of polymer may not effectively control the TDWS because only a portion of the optical mode is distributed in the cladding.
Furthermore, methods for suppressing TDWS for transverse magnetic (TM) mode was suggested before, but any method for effectively suppressing the TDWS for a transverse electric (TE) mode is not yet suggested. The TDWS suppression technique for the TE mode is essentially required in that silicon photonic devices mainly use a polarized light in the TE mode.